It is well known that nearly all compressors require a form of lubricant (e.g., oil) to cool, seal, or lubricate internal components. Typically, only static jet compressors and oil-free machines with rotors suspended in magnetic or air bearings are exempt from the need for some type of lubrication. In refrigeration systems that use compressors, a small portion of the compressor lubricant becomes entrained with the refrigerant and discharged from the compressor. The lubricant entrained in the refrigerant may cause several problems. For example, in a system with a single compressor, if too much lubricant is entrained in the refrigerant, the heat transfer and efficiency of the condenser and evaporator may be significantly reduced. In a system with two or more compressors, in addition to affecting heat transfer and efficiency of the condenser and evaporator, the entrained lubricant may not be returned to both compressors equally or properly, thereby providing too much lubricant to one compressor and too little to the other. This problem is exacerbated when the compressors are arranged in parallel.
Some conventional systems address this by using an oil equalization line system that connects the compressor crankcases or oil sumps via an oil equalization line. This approach usually requires the compressors having the same size and the same capacity and mounted at the same level or height. Other conventional systems use oil separators (either individual or common separators) to separate oil from the refrigerant and then return the separated oil back to the compressors. These systems are inherently complicated, more expensive and/or difficult to maintain and control.
Given the above background, there is a need in the art for climate systems and control methods that are simple, less expansive and/or easy to control and at the same time can realize the benefits of the parallel compressor configuration.
The information disclosed in this Background section is provided solely to provide a general background of the embodiments described herein and is not an acknowledgement or suggestion that this information forms part of the prior art already known to a person skilled in the art.